/*
 * @Author: long-xinyu2 2192763423@qq.com
 * @Date: 2025-03-11 18:47:55
 * @LastEditors: long-xinyu2 2192763423@qq.com
 * @LastEditTime: 2025-04-17 17:02:21
 * @FilePath: \algorithm\algorithm-training\2025_3_11.cpp
 * @Description: 这是默认设置,请设置`customMade`, 打开koroFileHeader查看配置 进行设置: https://github.com/OBKoro1/koro1FileHeader/wiki/%E9%85%8D%E7%BD%AE
 */
#include<iostream>
#include<cstring>
#include<vector>
#include<map>
#include<cstdio>
#include<algorithm>
#include<string>
#include<string.h>
#include<queue>
#include<math.h>
#include<set>
#include<functional>
#include<bits/stdc++.h>
using namespace std;
#define int long long
//using i128 = __int128_t;
inline int inc(int x, int v, int mod) { x += v;return x >= mod ? x - mod : x; }//代替取模+
#define endl '\n'
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int, int> PII;

const int N = 1500 + 10, M = 1e5 + 10;

inline int read()
{
    int x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9')
    {
        if (ch == '-')
            f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9')
        x = x * 10 + ch - '0', ch = getchar();
    return x * f;
}

int dp[N][N][2];

void solve()
{
    int n,m;
    cin >> n >> m;
    vector<vector<int>> arr(n + 10,vector<int>(m + 10));
    for(int i = 1; i <= n; i ++)
    {
        for(int j = 1; j <= m; j ++)
        {
            cin >> arr[i][j];
        }
    }
    int ans = 0;
    for(int i = 1; i <= n; i ++)
    {
        for(int j = 1; j <= m; j ++)
        {
            if(arr[i][j] == 1) {
                dp[i][j][1] = min(dp[i - 1][j][0],min(dp[i][j - 1][0],dp[i - 1][j - 1][1])) + 1;
            }
            else{
                dp[i][j][0] = min(dp[i - 1][j][1],min(dp[i][j - 1][1],dp[i - 1][j - 1][0])) + 1;
            }
            ans = max(ans,max(dp[i][j][0],dp[i][j][1]));
        }
    }
    cout << ans << endl;
}
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int tt;
    //cin >> tt;
    tt = 1;
    while (tt--)
    {
        solve();
    }
}